As surface treating methods using a photo-excitation process, the method of creating radicals by directly resolving the process gas molecule in the gas phase or the method of directly photo-exciting chemically bound molecules and/or atoms on the substrate surface to desorb them from the surface are already generally known. However, since a high photon energy is necessary to realize such phenomena, in fact vacuum ultraviolet of 20 eV or more and soft X ray of 100 eV or more had to be used. For example, a high-power excimer laser usable for the former and an electron storage ring to generate synchrotron radiation usable for the latter are very expensive and also punctual light sources. Therefore, their application for irradiating the substrate surface over a large area is difficult, and they are not put into practical use at the present moment.
And when the process gas comes into contact with the light sources of vacuum ultraviolet or soft X ray, the light sources are damaged. Therefore, it is desirable that the light sources are isolated from the process gas by an optical window. However, since there is no material suitable for an optical window through which light having an energy of 10 eV or more can be transmitted, the pressure of the process gas had to be suppressed to 0.0001 atmospheric pressure or lower, or a differential pumping mechanism or other complicated devices had to be used to achieve a pressure difference between the process chamber and the light source. In the case of the former, the reaction efficiency decreased remarkably, and in the case of the latter, the reaction area under light irradiation was limited down to several mm in diameter constituting a practical problem. And some other photo-excitation processes have been invented wherein ultraviolet of 4.9 eV and 6.7 eV emitted by a low-pressure mercury lamp is used in the place of such light sources. However, due to their extremely low reaction efficiency in the dissociation and ionization of molecules, they have not been put to practical use at the present moment.
The object of the present invention is to provide a method of treating an electrically conductive substrate by using a photo-excitation process wherein even a substrate surface having a large area in particular can be easily treated at a low cost.